The present invention generally relates to semiconductor processing, and in particular to a system for facilitating a uniform heating temperature of a photoresist.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as corners and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) is used to illuminate selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Due to the extremely fine patterns which are exposed on the photoresist, application and heating of the photoresist are significant factors in achieving desired critical dimensions. The photoresist should be heated such that a uniform heating rate is maintained in order to ensure uniformity and quality of the photoresist layer. The photoresist layer thickness typically is in the range of 0.1 to 3.0 microns. Good resist thickness control is highly desired, and typically variances in thickness should be less than xc2x110-20 xc3x85 across the wafer. Very slight variations in the photoresist thickness may greatly affect the end result after the photoresist is exposed by radiation and the exposed portions removed.
One of the variables in heating of photoresist film is the temperature at which heating occurs. In order to achieve uniform heating, a uniform temperature in a curing or enclosure chamber is necessary. Small changes in the time/temperature history of the photoresist can substantially alter image sizes, resulting in lack of image line control. A uniform time/temperature history of the photoresist is especially important with chemically amplified photoresists because image size control may be drastically affected by only a few degrees difference in temperature. Often substantial line size deviations occur when the temperature is not maintained within 0.5 degree tolerance across a silicon wafer. For example, when a photoresist is baked onto a substrate (e.g., wafer), temperature tolerances of xc2x10.2xc2x0 C. are required.
An efficient system/method to uniformly heat a layer of temperature-sensitive film formed on a semiconductor substrate is therefore desired to increase fidelity in image transfer.
The present invention provides for a system and method that facilitates uniform heating of photoresist formed on a semiconductor substrate (e.g., wafer). One aspect of the invention employs a heat transfer fluid to enhance the uniform heating of the photoresist. Heating elements are used to heat the heat transfer fluid, which in turn heats the wafer. The heat transfer fluid distributes the heat generated by the heating elements more evenly than conventional techniques, so as to eliminate hot and cold spots. The result is increased uniformity in heating of the wafer, and, thus increased uniformity in heating of the photoresist on the wafer. As a result of achieving substantial uniformity in heating of the photoresist, the fidelity of image transfer is increased.
One particular aspect of the invention relates to a system for facilitating a uniform photoresist heating temperature. At least one heating element operates to heat a heat transfer fluid. The heat transfer fluid is coupled to a substrate so as to heat a photoresist thereon. The heat transfer fluid can be any fluid suitable for transferring heat to the photoresist, such as a gas or a liquid. The system can include a shell for containing the heat transfer fluid. At least one heating element can be coupled to the shell, and the shell can be coupled to the substrate.
In another aspect of the invention, the system can include at least one temperature monitoring system for monitoring a temperature. At least one temperature monitoring system can provide temperature information of the heat transfer fluid. Alternatively, the at least one temperature monitoring system can provide temperature information of the photoresist. One temperature monitoring system can provide temperature information on the heat transfer fluid, and another temperature monitoring system can provide temperature information on the photoresist.
In yet another aspect of the invention, the temperature regulating system can include at least one temperature measuring system for measuring a temperature. At least one temperature regulating system can include at least one processor operatively coupled to at least one heating element. The processor can receive temperature data from the temperature measuring system. The processor can use the data to regulate the temperature of at least one heating element. At least one temperature measuring system can measure the temperature of the photoresist. Alternatively, at least one temperature measuring system can measure the temperature of the heat transfer fluid. At least one temperature regulating system can further include at least one temperature measuring system for measuring the temperature of the photoresist, and at least one temperature measuring system for measuring the temperature of the heat transfer fluid. The temperature measuring system can be any system suitable for measuring a temperature. At least one temperature regulating system can determine the existence of an unacceptable temperature based upon the determined temperature differing from an acceptable value.
Still another aspect of the invention relates to a system for facilitating uniform heating of a photoresist covering a substrate. The system comprises a plate for supporting the substrate. The plate comprises a surface for engaging a shell containing a heat transfer fluid, and at least one heating element operatively coupled to the plate for regulating temperature of at least portions of the photoresist, respectively, via heat conduction through the plate, shell, and substrate. The system further comprises a temperature regulating system for regulating temperature of at least a portion of the photoresist. The temperature regulating system comprises a temperature measuring system and a processor operatively coupled to the temperature measuring system and the at least one heating element.
In another aspect, the present invention can include a memory that stores acceptable temperature values for the photoresist. The processor can determine the existence of an unacceptable temperature for at least a portion of the photoresist based upon the measured temperature differing from an acceptable value. The processor can control at least one heating element to regulate the temperature of the photoresist portion.
Still yet another aspect of the invention relates to a method for facilitating uniform photoresist heating temperature. The method includes heating a heat transfer fluid to a temperature, and coupling a substrate with the heat transfer fluid so as to heat a photoresist to a temperature. The heat transfer fluid can be any fluid suitable for transferring heat to the photoresist. The heat transfer fluid can be contained in a shell, and the shell can be coupled to the substrate. The heat transfer fluid can be heated by at least one heating element coupled to the shell. At least one heating element can be inside the shell. At least one heating element can be outside the shell. The method can include regulating the temperature of the photoresist. The method can include regulating the temperature of the heat transfer fluid. Furthermore, the method can include regulating the temperature of the heat transfer fluid, and regulating the temperature of the photoresist. Alternatively, the method can include regulating the temperature of the at least one heating element.
Another aspect of the invention relates to a system for facilitating uniform heating of a photoresist. The system can include means for heating a heat transfer fluid to a temperature, and means for coupling the heat transfer fluid to a substrate so as to heat a photoresist to a temperature. The system can also include means for regulating the temperature of the photoresist. The system can further include means for regulating the temperature of the heat transfer fluid. Furthermore, the system can include both means for regulating the temperature of the photoresist, and means for regulating the temperature of the heat transfer fluid.
Still yet another aspect of the invention relates to a system for facilitating uniform heating temperature of a material. The system can include at least one heating element operative to heat a heat transfer fluid. The heat transfer fluid can be coupled to the material. The material can be a variety of materials including a top anti-reflective coating, a bottom anti-reflective coating, a low K dielectric material, spin on glass, a spin-on material.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.